Three squalene derivatives from Caulerpa prolifera

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IR &,$:ccm-‘: 3610, 3420 (OH), 1725, 1650 (C=CCO,R); MS m/z (ret. int.): 508 [Ml+ (0.3), 490 [M-H*O]+ (4), 408.178 [M - RC02H]+ (6) (C21H2808),83 [&H&O]+ (100). 55 [83 CO]’ (41); 589 [elk = +4.4

578 +5.0

546 +5.3

8 mg 8a were heated with 0.1 ml Ac20 for I hr at 70”. TLC (CH#&-C6H6-Et20, 2: 2 : I) afforded 4 mg 8b. colourless gum, MS m/z (rel. int.): 592 [Ml’ (0.2). 532 [M - HOAc]’ (4). 492 [M - RCO,H]+ (lo), 83 [C4H,CO]’ (100).

436 nm (CHCI,; c = 1.0). +8.4

Saponification (MeOH-H20-KOH, 70”) afforded L-inositol. L-Inosilol-2,3,5,6-tetra angelate and myoinositol-1,3,4,6tetra angelate. (6 and 7). Colourless gum, which could not

be separated into its constituents, IR ,z::crnml: 3610, 3480 (OH), 1720, 1650 (C=CCO,R); MS m/z (rel. int.): 508 [Ml’ (0.3), 490 [M-H,O]+ (2), 408.178 [M-RCO,H]+ (5) (C,4H280s) 83 [C4H,CO]+ (IOO), 55 [83 - CO]’ (44). Myoinositol-2, 4, 5, 6-tetra angelafe @a). Colourless gum, IR &~~cm--‘: 3610, 3440 (OH), 1730, 1250 (C=CCO,R); MS

m/z (rel. int.): 508 [Ml’ (0.3), 490 (4), 408.178 [M - RCOZH]’ (6) (C?,Hz808), 83 [C,H,CO]+ (100), 55 [83 -CO]+ (40);

Acknowledgements-We thank Dr. R. Gupta, University of Delhi, for plant material and the Deutsche Forschungsgemeinschaft for financial support.

REFERENCES

1. Baruah, N. C., Sharma, R. P.. Thyagarajan. G. and Herz, W. (1979) Phytochemistry 18, 2003. 2. Plouvier, V. (1963) in Chemical Plant Taxonomy (Swain, T., ed.) p. 323. Academic Press, London. 3. Bohlmann. F. and Zdero. C. (1977) Phytochemistry 16, 1243

589 [aI& = +3.4

578 +3.8

546 +4.0

4. Bohlmann. F., Mahanta, P. K.. Jakupovic, J., Rastogi, R. C. and Natu, A. A. (1978) Phytochemistry 17, 1165.

436 nm (CHCl,; c 0.74). +6.0

003 I-9422/82/030782-03$03.00/O 0 1982 Pergamon Press Ltd.

Phytochemistry. Vol. 21, No. 3, pp. 782-784, 1982

Printed in Great Britain.

THREE

SQUALENE

CA ULERPA LORENZO

DE NAPOLI,

Biorganica

dell’Universit8

FROM

PROLIFERA

ERNESTO FATTORUSSO*, SILVANA

Istituto di Chimica Organica e Biologica dell’Universit8 Chimica

DERIVATIVES

MAGNO

and LUCIANO MAYOL

di Napoli, Via Mezzocannone 16, 80134 Napoli, Italy; *Istituto di Napoli, Via L. Rodinb 22. 80138 Napoli, Italy

di

(Revised received 24 July 198 I) Key Word Index-Caulerpa prolifera; Caulerpaceae; (6s. 7S)-squalene-6,7-epoxide; (l0.S. I I S)-squalene. 10, 1I-epoxide; aII-trans-(3S)-2,6,1O,l5,19,23-hexamethy~~etracosa-l,6,10,14,18,22-hexaen-3-ol.

Abstract-(6S, 7S)-Squalene-6,7-epoxide, hexamethyltetracosa-1,6,10,14,18,22-hexaen-3-01

(IOS, 1lS)-squalene-10,l I-epoxide and all-trans-(3S)-2,6,10,15,19,23have been isolated from the marine alga Caulerpa prolifera.

Investigations of marine green algae of the family Caulerpaceae have resulted in the isolation of di- and sesquiterpenes [l-4]. From a member of this family, Caulerpa prolifera, we recently isolated (S)-( -)squalene-2,3-epoxide (1) [5], in addition to two acetylenic sesquiterpenes [l, 21. This is the first report of the occurrence in nature of 1, which is known to play an important role in the biogenesis of triterpenes and sterols. We wish to report here that this alga produces, in minor amounts, three structurally related

compounds, the epoxides 2. 3 and the allylic alcohol 4. Only 3 was previously isolated from a natural source (mycelia of Sclerotinia fructicola), but its stereochemistry was not determined [6]. The alga was freeze-dried and the chloroform extracts were purified by Si gel column chromatography. Individual components were then obtained by rechromatography on Si gel and by preparative AgNO,-Si gel TLC. Compounds 2. [a]‘,“- 11.2”, and 3, [a]g-- 3.8”, on

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783

5

6 the basis of their mass spectra [6] and ‘H NMR spectra, were tentatively identified as squalene-6,7epoxide and squalene-lO,ll-epoxide, respectively. These identifications were confirmed by comparison of their spectroscopic and chromatographic properties with those of two samples synthesized from all-trans-squalene with m-chloroperbenzoic acid according to Katayama and Marumo [6]. In order to clarify the chirality of C-6 and C-7 in 2 and C-10 and C-11 in 3, these compounds were treated with aluminium isopropoxide in boiling toluene. This highly regioselective reaction [7] afforded the two allylic alcohols 5 and 6. Application of the GC modification of the Horeau method according to Brooks and Gilbert [8] allowed the chirality of C-7 in 5 and C-11 in 6 to be determined as S, thus revealing the stereochemistry of C-7 in 2 and C-11 in 3.

The absolute configurations of the tertiary carbon atoms of the oxirane rings in 2 and 3 were established by the following observation. The synthetic squalene6,7-epoxide and squalene-10,l I-epoxide were identical chromatographically and spectroscopically to 2 and 3, and on the basis of the stereochemistry of the epoxidation with peracids [9], these must be racemic mixtures of (6R, 7R)- and (6S, 7S)-squalene-6,7epoxide and (lOR, 1lR)- and (lOS, 11S)-squalenelO,ll-epoxide. Considering that the stereochemistry of C-6 in 2 and C-10 in 3 was established as S, 2 and 3 must be (6S, 7S)-squalene-6,7-epoxide and (lOS, 11S)-squalene-10,l I-epoxide, respectively. Compound 4, isolated in a yield of 0.003%, [a]glO.O”, had the molecular formula C,oH,oO (precise mass measurement). Its ‘H NMR spectrum indicated the presence of seven vinylic methyl groups (a set of seven overlap-

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784

ping signals from 6 1.73 and 1.60, 21 H), seven olefinic protons (5.15, 5H, complex signals; 4.94, lH, m; W,,,=6Hz; 4.81, lH, m; W,,?=7Hz) and one ailylic )CHOH

group

(4.05, 1H, t, J = 6 Hz).

On the basis of these data, structure 4 was tentatively assigned to this compound. This assignment was confirmed by comparison with an authentic sample prepared from (S)-( -)-all-truns-squalene-2,3epoxide, isolated from the same source, by treatment with aluminium isopropoxide in boiling toluene.

EXPERIMENTAL

General procedures. The ‘H NMR spectra were measured at 270 MHz with TMS as internal standard; CDC& was used as solvent. Mass spectra were taken with a direct inlet system. Extraction and isolation of constituents. The alga (700g fr. wt) collected in June 1980 in the Bay of Salerno, Italy, was freeze-dried and ground to a fine powder with a blender. The dried alga was extracted x 3 with CHCIX with continuous stirring. The extracts were combined and evapd to give a dark-green oil (I5 g). The crude extract was applied to a column (5 x 120 cm) of Si gel. The column was eluted with a solvent gradient from hexane to hexane-Et*0 (9: 1). Fractions of 2OOml were collected. The following compounds were isolated in order of increasing polarity. (6S, 7S)-Squalene-6,7-epoxide (2) and (lOS, 1 lS)-squalenelO,ll-epoxide (3). Fractions 20-22 were pooled and subjected to column chromatography (Si gel, I x 60 cm) using as eluant a gradient system of hexane-C6H6 from 8: 2 to 6:4. Fractions of 20 ml were collected. Fractions 19-21, evapd to dryness, afforded 25 mg of an oily material which was further fractionated by prep. TLC (AgNO1-Si gel, C6H6EtOAc, 7 : 3) to give pure 2 (6.5 mg) and 3 (8 mg). 2, [aIF11.2” (CHCI1; c 0.100). M+ 426 m/z, 6 5.12 (5H, br, vinyl protons), 2.71 (IH, t, J = 6 Hz, H-7) and 1.26 (3H, s, Me-6). 3, [a]$-3.8’(CHCIs; c O.lOO), M’ 426 m/z, fi 5.11 (SH, br. vinyl protons), 2.74 (IH, t, J = 6 Hz, H-II) and 1.26 (3H, s, Me-IO). All - trans - (3s) - 2,6,10,15,19,23 - hexamethyltetrucosa 1,6,10,14,18,22-hexaen-3-ol (4). Fractions 28-30 were rechromatographed on prep. TLC (Si gel hexane-Et,O, 9: 1) to give 4 as an oily residue (21 mg). [a]?10.0” (CHCIj; c 0.100); MS m/z 426.3841 (M’, talc. for CJ~H~,,O, 426.3860). Treatment of 1, 2 and 3 with aluminium isopropoxide. To a soln of 1 (20 mg) in 3 ml dry toluene, AI(OCHMe2)j (15 mg) was added and the mixture refluxed for 10 hr. After addition

Reports of Hz0 the organic phase was separated and taken to dryness. The crude product was purified by prep. TLC (Si gel, hexane-EtOAc, 17: 3) to give I4 mg of 4. 2 (3 mg) and 3 (3 mg) were treated with AI(OCHMe2)1 and the reaction mixtures purified in the same experimental conditions described above to give 5 (2 mg; M’ m/z 426; S 5.13, IH, m, W1,2=6H~ and S 4.94, lH, m, W,,Z=6Hz, =CH,: m/z

S 4.04, 426;

IH,

S 5.00.

\

t, J = 7 Hz. ,CHOH) lH,

m,

WI,:=6

Hz

and 6 (2mg,

and 4.93. \ W,,? = 6 Hz, =CHZ; 4.04, lH, t, J = 7 Hz, ,CuOH).

IH,

M’ m.

Application of the GC modificution of the Horeau method to 4 and 5. Compound 4 (2 mg) in dry pyridine (4 ~1) was treated with an excess ( i )-a-phenylbutyric anhydride and was kept at 40” for 1.5 hr. Conventional work-up [8] led to the isolation of a preponderance of (R)-a-phenylbutyric acid. Compound 5 (2mg) in the same experimental conditions of (R)-ndescribed above also gave a preponderance phenylbutyric

acid.

Acknowledgements-This work is a result of research sponsored by the Consiglio Nazionale delle Ricerche (Rome) in the Programme of the ‘Progetto Finalizzato per I’Oceanografia e i Fondi Marini’. Thanks are due to the Centro di Metodologie Chimico-fisiche of the University of Naples (Mr. I. Giudicianni) for the determination of ‘H NMR spectra. REFERENCES

I. Blackman. A. J. and Wells, R. J. (1976) Terrahedron Letters 2729. 2. Blackman, A. J. and Wells, R. J. (1978) Tetrahedron Letters 3063. 3. Amico, V., Oriente, G., Piattelli, M., Tringali, C., Fattorusso, E., Magno, S. and Mayol, L. (1978) Tetrahedron Letters 3593. 4. De Napoli, L., Fattorusso, E.. Magno. S. and Mayol, L. Experientia (in press). 5. De Napoli, L., Fattorusso, E.. Magno. S. and Mayol, L. (1980) Tetrahedron Letters 2917. 6. Katayama. M. and Marumo, S. (1979) Tetrahedron Lerters 1293. 7. Terao, S., Shiraishi, M. and Kate, K. (1979) Jpn. Kokai Tokkyo Koho 7.16, 507. 8. Brooks, C. J. W. and Gilbert. J. D. (1973) J. Chem. Sac. Chem. Commun. 194. 9. Gould, E. S. (1959) Mechanism nnd Structure in Organic Chemistry, p. 534. Holt, Rinehart & Winston. New York.